What's New?

Updated April 2014

Surface remedy construction on the Captain Jack Mill Superfund site fared very well in the September 2013 flood event. The surface remedy was physically completed in November 2012. The remedy consisted of consolidating mine waste materials from various areas of the site into two consolidation cells. One cell is located at the former Captain Jack Mill area and the other is at the Big Five Waste Rock Pile area. Vegetated soil cover systems with surface water diversion structures were established over each consolidation cell to prevent human contact with contaminated materials and to minimize rain and snow melt contact with the waste materials, to prevent leaching of metals into the surface water. Areas from which contaminated materials were excavated were seeded with native grasses and plants. The vegetation was well established by August of 2013, which ensured the remedy was functional in resisting erosion that can be caused by large rain events.

Design for the subsurface remedy to address the Big Five adit acid rock drainage discharge was completed in September 2013. Remedy construction is anticipated to take one field season, followed by two to three years of monitoring to determine if additional treatment is needed. The start of construction on the subsurface remedy is dependent upon the availability of federal funding, which is not anticipated in 2014.

Site Description

The Captain Jack Mill site is located at the headwaters of upper Left Hand Creek about 1.5 miles south of Ward in Boulder County, Colorado. The site is in a narrow valley known as California Gulch. Mining for gold and silver in the region began in 1860 and ended in 1992.

At the time of listing, the site included the Big Five Mine (the upper mine), Captain Jack Ltd. Mill, the Black Jack Mine, and other mines and waste features in the immediate surrounding area. The Big Five Mine, located about 500 feet upstream from the Captain Jack Mill, consisted of a discharging adit (tunnel), a large waste rock pile and a settling pond. The mill works area included several constructed ponds previously used for settlings tailings from the mill operations.

In September 1986, the Mine Safety Health Administration found improper storage of chemicals at the mill buildings. EPA removed several drums of chemicals and concentrated mine wastes in March 1987.

Big Five Mine (foreground) and the Captain Jack Mill area (background) at the turn of the 20th century

The Colorado Mined Land Reclamation Board received reports of dumping of mine and mill wastes into Left Hand Creek in October 1992. At the same time, a milky white substance was reported in Left Hand Creek. Tailings-like material was observed entering Left Hand Creek from the unlined tailings ponds, turning the creek a milky gray color for about six miles downstream.

Sampling of the discharge to the creek found high levels of zinc, cadmium, copper and lead. The Left Hand Water District shut off their drinking water intake 15 miles downstream on Left Hand Creek. CDPHE issued a Notice of Violation and a Cease and Desist Order. The Colorado Department of Minerals and Geology (CDMG) obtained a restraining order to prevent further mill operations.

CDMG determined in 1993 that there was a threat to the environment from the tailings through blowing dust, surface flooding, overflow of the tailings pond and subsurface groundwater percolation. They also determined that there were improperly stored drums and explosives. A 1997 EPA inspection found elevated levels of heavy metals in the soils from the Big Five Mine waste pile and settling pond and in the unlined tailings lagoons at the Captain Jack Mill. EPA also confirmed the findings of earlier elevated levels of metals in the Big Five adit drainage.

Site Risk

The Left Hand Water District uses water from Left Hand Creek as a drinking water source. Their water intake has not been impacted by the site, but the potential for contamination exists in the future. The Town of Ward’s drinking water supply is located up-gradient and is not impacted by the site.

Cleanup Progress

In June 2008, EPA and CDPHE completed the site's final Remedial Investigation and Risk Assessment report and Feasibility Study report (RI/FS). The FS report contains a detailed analysis of remediation alternatives for various site components. The proposed plan presented EPA's and CDPHE's preferred alternative for the remediation of the site. A public meeting was held July, 2008 giving the community a chance to comment on the preferred remedy. From this process a remedy was selected for the site and documented in the Record of Decision (ROD) signed on September 29, 2008. The selected remedy described in the ROD was further modified by an Explanation of Significant Differences (ESD) signed on October 2011.

Overview of Selected Remedy

The selected remedy for cleaning up the Captain Jack Mill Superfund Site has two components, as it addresses both surface and subsurface contamination sources.

Surface

Under the surface remedy selected in the ROD, mine waste materials were to be excavated and placed in on-site consolidation cells. The selected remedy called for excavation of all mine waste material containing contaminants of concern in concentrations above the remedial action levels.

Surface remedy construction on the Captain Jack Mill Superfund site began in June 2012 and was physically completed in November 2012. A one year operable and functional period determined that the surface remedy was functioning as intended. The remedy consisted of consolidating mine waste materials from various areas of the site into two consolidation cells. One cell is located at the former Captain Jack Mill area and the other is at the Big Five Waste Rock Pile. Vegetated soil cover systems with surface water diversion structures were established over each consolidation cell to prevent human contact with contaminated materials and to minimize rain and snow melt contact with the waste materials to prevent leaching of metals into the surface water. Areas from which contaminated materials were excavated were seeded with native grasses and plants. Buildings associated with the previous Captain Jack Mill operations were demolished during the construction of the consolidation cell.

By the end of the first growing season, the alpine prairie type vegetation was well established. The cover system performed very well in the September 2013 flood event. The remedy, including the road and water diversion structures, sustained only three localized areas of erosion that required mitigation.

Operation and Maintenance: CDPHE will conduct inspections of the cover systems on an annual basis. Repairs required to mitigate erosion or other damage will be conducted by CDPHE as needed.

Big Five Waste Rock Pile before the remedial action (left) and after the remedial action (right)

Subsurface

To address subsurface contamination, the remedy (Alternative 3B in the RI/FS) consists of an installed bulkhead, mine pool treatment, and the option for phased biochemical reactor treatment. The concrete bulkhead will plug the draining mine adit, impounding the mine water. A section of the tunnel will be packed with crushed limestone to introduce alkalinity to neutralize the water. The mine pool environment will have reduced oxygen levels which, coupled with the added alkalinity will increase the pH of the water to a neutral condition causing most metals to precipitate from the water as solids (Phase I). Additional flexibility has been added to the design. If additional pH adjustment is needed in the future a compound like sodium hydroxide can be injected into the tunnel. Also water can be recirculated through the crushed limestone section promoting mixing of the water to promote treatment.

During the design work, additional site investigations were necessary including geotechnical testing within the Big Five tunnel, geophysical investigations to determine the location and extent of the tunnel system, and borehole installation for groundwater monitoring and tunnel locating. Access was requested and granted from property owners to conduct this testing.

Because of uncertainties over the mine workings, there will be extensive groundwater monitoring once the bulkhead is installed. If necessary, after approximately two to three years of mine pool treatment, EPA and CDPHE may install a series of biochemical reactors outside of the mine (Phase II) as a means of additional treatment or polishing of the water. These reactors use microorganisms to immobilize metals thereby removing them from the treated water. The treated water would flow by gravity to Left Hand Creek.

Community Involvement

Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, on-going, meaningful community involvement. The goals of the Superfund community involvement program are to:

Keep communities affected by sites informed throughout the cleanup process

Provide opportunities for communities to comment and offer their input about site cleanup plans

Facilitate the resolution of community issues tied to a site

EPA and CDPHE provide the public with information about the cleanup of the Captain Jack Mill Superfund Site through fact sheets, press releases, public meetings, and public notices published in the local newspaper. The site community involvement plan was last updated in November 2009. EPA and the CDPHE also maintain information in the Site Information Repository, located at the Boulder Public Library, and also at EPA, CDPHE and Boulder County Health Department offices. Site documents, including the most recent status update fact sheet, can also be viewed in Site Documents below.

The CDPHE, EPA and the Lefthand Watershed Oversight Group (LWOG) have hosted meetings with community members to update them on site activities and proposals. Local citizen volunteers have formed the Lefthand Creek TAG Coalition (LCTC) to monitor the cleanup of the Captain Jack Mill site. Aided by a Technical Assistance Grant (TAG) of $50,000 from EPA, LCTC hired an independent technical advisor to help interpret and comment on site-related information.

Reuse

EPA places a high priority on land reuse as part of its Superfund response program mission. The Agency tries to select cleanup options that encourage and support future use of a site. We use two fundamental methods to facilitate reuse of Superfund sites:

Exploring future uses before the cleanup remedy is implemented, an approach that gives the Agency the best chance of designing cleanup remedies to support the likely future use of a site

Working with landowners and communities to remove barriers not considered necessary for the protection of human health or the environment at those sites where remedies are already in place

One option for reuse is the siting of clean and renewable energy projects on contaminated (or formerly contaminated) lands. As part of this effort, EPA is evaluating the potential for energy projects on these properties and working with landowners and communities to identify ways to remove barriers to such projects.

At the Captain Jack Mill site, property is owned by both private and public entities. A portion of the site is owned by the Boulder County Open Space. This green space helps protect the watershed and connects contiguous sections of subalpine habitat. EPA and CDPHE will continue to look for reuse opportunities in cooperation with the various property owners.

Land Use Controls and Other Institutional Controls

Land use controls are the most common type of institutional control (IC). ICs are administrative or legal controls that help reduce the likelihood for human exposure to contamination. ICs can also help protect the integrity of the remedy. Examples of ICs are:

Zoning ordinances

Environmental covenants

Deed notices

Well-drilling restrictions

Building permits

Informational advisories

An environmental covenant, administered by CDPHE, will be put in place to protect the remedy features from incompatible uses. Well-drilling may also be restricted around the property. The effectiveness of these ICs will be reviewed during the five-year review process or on a more frequent interval if necessary.

Five-Year Reviews

EPA or the lead agency conducts five-year reviews following the start of a Superfund cleanup when contamination is left on the site. These reviews are repeated every five years. We use these reviews to determine:

How the remedy is working

If the remedy remains protective of human health and the environment

The first five-year review for this site is scheduled to be completed in 2017.